The invention pertains generally to dc/dc power converters and specifically to a balanced converter which provides a dc output voltage that tracks the amplitude and phase of a sensed audio signal.
The efficiency of a linear RF power amplifier is improved when the dc voltage that is applied to the RF power amplifier tracks the audio signal that also modulates the RF signal that is to be amplified by the power amplifier. This tracking of the input audio signal by the power supply that is modulating the excitation to the power amplifier results in the power amplifier maintaining a constant collector-to-emitter voltage across its output transistors. Although the prior art power converters that provided buck (output dc voltage is less than the dc input voltage) and boost (dc output voltage is greater than the dc input voltage) and/or both buck and boost, lend themselves to the above application, the prior art dc-to-dc converters (such as that disclosed in U.S. Pat. No. 3,898,549) were not able to respond linearly to the full audio range of signals, especially as the frequency of the audio input signal approached 20 KHz. To be linear, when tracking signals having a frequency at or near 20 KHz, the switching frequency of an inverter associated with the dc converter must be around 100 KHz which corresponds to a full-wave rectified output frequency of 200 KHz or 10 times the highest signal frequency. The maximum duty cycle of the pulse-width modulated signals of the prior art dc-to-dc converters is about 0.8, which corresponds to the maximum dc voltage output with a minimum dc voltage input. The conductive time under the condition of minimum output voltage, corresponding to minimum input audio signal, and maximum input voltage is typically 1.2 .mu.s at a 200 KHz switching frequency. This time is much shorter than the typical storage time of the bipolar transistors in the switching inverter of the dc/dc converter. Consequently, this phenomenon precludes a linear modulated response of the dc-to-dc prior art converters.